Geology Reference
In-Depth Information
Mineral alignment
Layering
modal mineral variations
Schlieren
Mafic mineral aggregates
Figure 7.7
Schematic diagram highlighting some of the common crystal and
crystal aggregate planar and linear fabrics.
7.4.2 Crystal plastic strain fabrics
Otherwise superficially quite similar planar fabrics can also be developed
when plutonic rocks are subjected to regional deformation after the magma
has crystallised (but not necessarily cooled to ambient temperatures). These
are commonly S-C type fabrics located near the margins of plutons, or close
to internal fault zones or contacts between different magma types. S-C fabrics
comprise two contemporaneous planar foliations, an S-plane defined by the
grain shape fabric, and a crenulation or shear plane (C). When observed
correctly (that is normal to foliation in the X/Z plane of the strain ellipse
and parallel to lineation), then the angle of intersection between the S and C
